A parking brake system of a car is mainly used to keep the car motionless when it is parked. The traditional parking brake system is hand-operated and thus named “handbrake”. The driver needs to control the force of pulling the handbrake based on experience.
Electric parking brake (EPB) systems have been gradually replacing the traditional mechanical handbrakes. The existing EPB system includes a motor, an actuator connected with the shaft of the motor, and a brake mounted on a wheel of the car. The operation of the actuator is transmitted through a lead screw or a ball screw. To perform a brake operation, the driver needs only press an electric button to operate the motor which drives the actuator, which causes the lead screw or ball screw to rotate to apply the brake, thus braking the car. However, the lead screw transmission results in low transmission efficiency. While the ball screw can increase the transmission efficiency, the brake system cannot be self-locked so that brake may be released after the actuator is turned off allowing the car to roll away after the brake has been applied.